Background in Mechanical, Electronic, and Systems Engineering.
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Here are two methods to bleed your brakes without pulling your hair out in the process.
The fact that you’ve found this guide means you’ve likely run into a problem getting your brakes working after replacing your master cylinder or caliper. The normal “pump and release” method just doesn’t work. Even bleeder pumps have about a 50/50 rate of success without knowing the system well.
The good news is that your new part isn’t defective. And the rest of the parts in the system are most likely fine too.
These models can be particularly difficult:
- Yerf Dog Spiderbox GX150
- Tomberlin Crossfire 150 and 150R, and Punisher models
- Twister Hammerhead 150cc Karts
Two Good Bleeding Options
Upside: Free and Fast
Downside: Requires disassembling the master cylinder (voiding warranty)
This is a technical process and you’ll have a few prep steps. But once you get the hang of it, you’ll appreciate the time it saves you when you need do brake work in the future.
Vacuum Pump (High Volume)
Upside: No disassembly required. Won’t void the warranty.
Downside: Cost of the vacuum tool
Simpler than the first option, but you’ll need to shell out another $25 or so for a pump, and in this end this has a chance of not working.
Which method you choose is up to you. We’ll cover both below. You can skip straight down to the vacuum pump method if you prefer.
How to Bench Bleed
If you just bought a new master cylinder, and aren’t worried about voiding warranty, bench bleeding is the fastest and most reliable method of getting all of the air out of the system. If you master cylinder is older and dirty, be sure to thoroughly clean it before disassembly.
Although the name implies that you’ll need to remove the whole system, you don’t actually have to. You can still use this method while most of the system is on the kart. At a minimum you’ll need to remove the master cylinder.
Gather these items
- 12″ minimum of clear fuel hose
- An 8mm wrench
Unmount the Master Cylinder
Remove the bolts holding the master cylinder to the kart. Don’t remove any brake lines from the master cylinder.
If you haven’t already, clean the master cylinder now.
Remove the Piston
Most master cylinders have a retaining clip holding the piston and internal spring. Carefully remove this clip, you’ll need to reuse it.
Take notes (mentally or on paper) of the order of the internal components, so you’ll know how to re-assemble when you’re done.
Drain the remaining brake fluid
Using the clear hose, drain the brake system entirely at each caliper into an appropriate container for disposal.
Flip your master cylinder so that the open chamber is upwards, with all brake lines as low as possible. Secure it in this position using zip-ties or similar, as high as possible above the rest of the system.
With the master cylinder positioned like this, you can see that what we’re doing is using the open cylinder as a “cup” that you’ll keep full in the next steps. Since the piston is removed, there is nothing preventing the fluid from flowing freely to the tip of the caliper bleeder. This is important.
This method works very well due to the rapid flow of brake fluid that will be passing through the system. Air doesn’t get a chance to bubble it’s way back into high spots in the lines.
Grab your DOT3 or DOT4 Fluid
It doesn’t matter which you use, as long as you’ve completely drained out the old fluid.
Fill the reservoir
Fill your master cylinder and seal it securely. If you have a master cylinder with a built-in reservoir, you’ll need to use a finger to block the internal reservoir passage inside the master cylinder, while filling the reservoir from above. Once it’s filled and the cap is on tight, you’re ready to get started bleeding.
Open the rear caliper bleeder
If you have front calipers, make sure their bleeders are closed. Use your clear hose and very clean container to catch the fluid coming out of the bleeder/hose.
- Once you start pouring, you can’t allow the fluid level in the cylinder to lower pass any of the port holes for the brake lines.
- Pour smoothly to avoid stirring up bubbles in the cylinder
Have a friend watching the flow out of the caliper, with a hand on the bleeder ready to tighten it. Fluid will be moving quickly, they’ll need to be ready for when you say tighten.
Continue to pour until no more bubbles come out (visible in the clear length of hose). You can keep pouring for a bit more if you like. When you’re ready, give the signal to close the bleeder.
If you only have rear brakes, you’re done bleeding and can start putting everything back together.
Bleeding the front brakes
Bleeding front brakes is the same process as the rear. Repeat for each caliper in the system.
When finished with all calipers, reassemble the master cylinder and test for pressure. If you run into any problems, leave a comment in the section below.
The key to success with a vacuum pump, is to make sure that you continuously pull a large amount of fluid through the system rapidly. Since instructions should come with the pump unit that will cover its general operation, we’ll focus on how to get the best results in this case.
Teflon Tape around the bleeder threads
The threads on the bleeder aren’t designed to seal. So when you use a vacuum pump, it will pull air from around the threads and into your line. This will give the appearance that the system never runs out of bubbles, and you won’t get proper suction on the system.
Use teflon tape to temporarily seal the threads.
Build up suction with the bleeder closed
To get the maximum fluid flow, build up suction with your pump before opening he bleeder.
Maintain suction continuously, as much as possible. Your pump unit should have a gauge, keep it maxed out if possible.
It helps to have a helper refilling the master cylinder’s reservoir as it lowers. Never allow the reservoir to run out of fluid, or you’ll have to repeat the whole process.
Even with these tips, using a vacuum pump may just not work. In this case, use the bench bleeding method in this article.
Leave your thoughts in the section below!